In the field of LCDs, backlight systems have been widely utilized for illuminating a liquid crystal layer from its back for light emission. A known LCD has a backlight unit placed on the underside of a liquid crystal layer. Such a backlight unit 20 is generally comprised of, as shown in FIG. 8, a bar-like lamp 21 (light source); a light guide plate 22, in the form of a square plate, placed with one end extending along the lamp 21; a light diffusion sheet 23 placed on the surface of the plate 22; and a prism sheet 24 placed on the surface of the sheet 23.
In the backlight unit 20, light beams (ray) emitted from the lamp 21 and incident on the plate 22 are reflected off the side faces of the plate 22 and reflective dots or a reflective sheet (not shown) on the rear face of the plate 22 and then go out of the surface of the plate 22. The light beams (ray) transmitted from the plate 22 are incident on the sheet 23, diffused, and then, go out of the surface of the sheet 23. Thereafter, the light beams from the sheet 23 are transmitted to the prism sheet 24 and then allowed by a prism section 24a formed on the surface of the sheet 24 to go out as light beams that form a distribution with a peak at an upward direction substantially normal to the sheet 24. The light beams from the lamp 21 are diffused by the sheet 23 and, then, refracted by the sheet 24 so as to form a distribution peak at an upward direction substantially normal to the sheet 24 to illuminate the entire surface of the liquid crystal layer (not shown) disposed in an upper position.
With reference to FIG. 9, there is provided another type of backlight unit 20 which is designed, in view of the light collecting properties of the prism sheet 24, such that another light diffusion sheet 23 or prism sheet is disposed on the surface of the sheet 24.
The known light diffusion sheet 23 commonly employed in the backlight unit 20 comprises, as shown in FIG. 10, a light diffusion layer 26 containing beads 29 dispersed within a binder 28; a transparent base material sheet 25; and a sticking-inhibiting layer 27 containing beads 31 dispersed within a binder 30, light diffusion layer 26, base material sheet 25 and sticking-inhibiting layer 27 are laminated in this order.
The binder 30 used for the sticking-inhibiting layer 27 is poor in wear resistance and liable to scratch defects. In addition, since the beads 31 are dispersed in the binder 30, there is a risk that the rear face of the light diffusion sheet 23 is easily damaged or deformed, resulting in depreciation of its commercial value, if a plurality of light diffusion sheets 23 are stacked together on top of one another during manufacture, delivery, storage, and the like, of the light diffusion sheets or if the light diffusion sheet 23 is laid over the irregular surface of the prism sheet, when incorporated into the backlight unit 20.